A semiconductor memory device is a storage device that stores data and reads the data, if necessary. Semiconductor memory devices are largely classified into two groups, volatile memory devices and nonvolatile memory devices.
Volatile memory devices are memory devices that lose stored data when power source is interrupted. Volatile memory devices include, for example, Static Random Access Memory (SRAM), Dynamic Random Access Memory (DRAM), and Synchronous DRAM (SDRAM). Nonvolatile memory devices are memory devices that hold stored data even when power source is interrupted. Nonvolatile memory devices include, for example, Read Only Memory (ROM), Programmable ROM (PROM), Erasable PROM (EPROM), Electrically EPROM (EEPROM), flash memory device, Parameter RAM (PRAM), Magnetoresistive RAM (MRAM), Resistive RAM (RRAM), and Ferroelectric RAM (FRAM). Flash memory devices are largely divided into two groups, NOR type flash memory and NAND type flash memory.